In addition to the strong demands for silver halide photographic light-sensitive materials to make sensitivity and image quality higher especially in excellent graininess and sharpness, there have further been the strong demands for a proper low replenishment-rate process for the reduction of environmental pollution, a rapid process for answering the demands for short-time photofinishing services, and so forth. These demands may mostly be answered in the case that the high sensitization of silver halide grains may be achieved. It is, therefore, not too much to say that the increase in sensitization of silver halide grains has been the very issue of the most important for the industry concerned.
There have heretofore been a number of studies on the high sensitization of silver halide grains. To be more concrete, there have been the studies such as those of the methods of chemical sensitization and spectral sensitization. Among them, the following methods have been well known.
The well-known highly sensitizing method techniques of a chemical sensitization include, for example, those using a sulfur sensitization, a noble-metal sensitization such as a gold sensitization, a palladium sensitization, a platinum sensitization, an iridium sensitization and a selenium sensitization, a reduction sensitization or the like, each of which may be used independently or in combination.
As for the well-known spectral sensitizing dyes applicable to spectral sensitization, there are optical sensitizers including, for example, such a cyanine or merocyanine dye as a zeromethine dye, a monomethine dye, dimethine dye, a trimethine dye and so forth, each of which may be used independently or in combination to be used for a supersensitization, for example.
These techniques are also described in, for example, U.S. Pat. Nos. 2,688,545, 2,912,329, 3,397,060, 3,615,635 and 3,628,964, British Pat. Nos. 1,195,302, 1,242,588 and 1,293,862, West German OLS Pat. Nos. 2,030,326 and 2,121,780, Japanese Patent Examined Publication Nos. 4936-1968 and 14030-1969, and so forth.
Among these techniques, a spectral sensitization technique is indispensable to practically applicable light-sensitive materials and, more particularly, to color light-sensitive materials, because these light-sensitive materials contain the silver halide grains intrinsically sensitive to blue-light and, besides, to green-light or red-light.
One of the ways of obtaining a high sensitivity through a spectral sensitization is to select the conditions for a suitable combination of the above-mentioned chemical sensitization and spectral sensitization. However, even if only this way is taken, it is still not satisfactory to answer the aforementioned demands for light-sensitive materials.
One of the other ways is to select a suitable sensitizing dye. However, there are a number of requirements which should be satisfied by sensitizing dyes applied to photographic light-sensitive materials. Namely, not only a high spectral sensitivity should simply be obtained, but also, in the case of adding such a dye into a silver halide emulsion, any fog should not be increased, spectral charachteristics should be excellent, the excellent characteristics at the time of exposure including an excellent latent image stability, a few dependability on temperature and humidity at the time of exposure and so forth should be obtained, a few fog increase and a few variation in sensitivity and gradations should be retained in the preservation of raw products which are light-sensitive materials before an exposure and development are applied thereto, the so-called dye contamination caused by the dyes remaining in a light-sensitive material even after a development process should be minimized, a preparation stability should be excellent and so forth. It is very difficult to select suitable sensitizing dyes which can satisfy all of the above-mentioned requirements.
As for one of the further ways, it has been known that a supersensitization is useful. Such supersensitization is described in, for example, `Photographic Science and Engineering`, Vol. 13, pp. 13-17, 1969; ibid., Vol. 18, pp. 418-430, 1974; T. H. James, `The Theory of the Photographic Process`, 4th Ed., Macmillan Company, 1977, p. 259; or the like, from which it has been known that a high sensitivity may be obtained by choosing suitable sensitizing dyes and supersensitizers.
From the results of the experiments conducted by the inventors, it was found that, when a sensitivity is made higher so as to satisfy the aforementioned demands for light-sensitive materials, the sensitivity was lowered and the fogginess was increased both seriously during the period of preservation; the reason is still not clarified though. The deteriorations of the characteristics of a raw product is a defect that is fatal for a light-sensitive material for which is strongly demanded to make the characteristics thereof uniform.
The other techniques of improving the preservation stability of such raw products are disclosed in, for example, Japanese Patent Publication Open to Public Inspection (hereinafter called Japanese Patent O.P.I. Publication) Nos. 43320-1973, 176637-1983, 225143-1985, 225145-1985, 232545-1985, 112143-1986, 91652-1986 and 203447-1986, and so forth. Any of these techniques is not satisfactory to improve both of the sensitivity variations of raw samples in preservation and the fog variations, while retaining a high sensitivity.
Meanwhile, in recent years, an automatic photofinishing machine compact in size which is so-called `Mini-Lab` by which a photofinishing from color negative development to color print can be performed in a narrow space. As such a `Mini-Lab` is getting popular, it has been innegligible that the fluctuation in sensitivity of a light-sensitive materials caused by fluctuation of environmental humidity at the time of exposure mentioned above.
At such a Mini-Lab as mentioned above, the numbers of light-sensitive materials to be processed are comparatively smaller than those of large-scale photofinishing laboratories. It is, therefore, difficult to keep the characteristics of processing solutions constant. It takes a long time to use up a bulk of color paper loaded. The temperature and humidity conditions are apt to be fluctuated at the time of printing, because processing apparatuses are often installed close to the store front.
Mini-Labs have, therefore, such a defect that high-quality images may not easily be obtained.
The present inventors devoted themselves to studying on the above-mentioned problems confronting Mini-Labs and so forth and, resultingly, the inventors found that, when a color paper being in a humid-equilibrium at a certain humidity is moved to a place at a different humidity, it will require about one hour to have stable characteristics even in the portion of color paper exposed directly to the air and, at this time, the fluctuation of sensitivity was several tens of percentage. The inventors also understood that these findings may not be neglected as the factors of the characteristic fluctuation.
The humidity influence at the time of exposure is described in detail in T. H. James, `The Theory of the Photographic Process`, 4th Ed., Chap. 2, Macmillan Co., 1977. There is the description of a process in which pAg of an emulsion layer is lowered. In this process, photographic characteristics are seriously deteriorated and almost no sensitivity fluctuation inhibition effect may be displayed.